Question LGA1851 with 2 x PCIe5.0 SSD support, without affecting GPU lanes.

[MnsoonMally]

I'm currently speccing-up a new build PC, both for Gaming, and for Production work.

I'm looking at all 3 ranges of technology, i9, Core Ultra, and AMD.

For Core Ultra, I'm looking to clarify identification of motherboards (if any) that fully support 2 x PCIe5.0 SSD's, WITHOUT, taking anything away from the GPU.

I've made an Excel spreadsheet with around the top dozen or so Motherboards currently available - but the clarity of which supports what SSD's without affecting the GPU is still somewhat unclear, even using the manuals.

I'm aware that 'you won't be able to tell the difference' between PCIe5.0 and PCIe4.0; but that's not my question - I'm looking specifically for Motherboards that support 2 x PCIe5.0 SSD's, without taking lanes from the GPU.....if any exist.

 

[faalin]

It would be more helpful if you listed the boards you are looking at. But from the three i looked at

MSI z890 tomahawk from CPu runs a PCIe 5.0 and 4.0
ROG Maximus z890 Extreme has to PCIe 5.0 slots, but if ether M.2_3 or M.2_4 are populated the PCIex16_1 will drop to 8x.
Asrock z890 Taichi Aqua same thing if second M.2 5.0 is installed the PCIex16 slot drops to 8x


I would have to say if those two $900+ boards Asus and Asrock cant do it then none of them will.

 

[MnsoonMally]

Only definitive answers, (if any), please.

If:

'I'm looking to clarify identification of motherboards (if any) that fully support 2 x PCIe5.0 SSD's, WITHOUT, taking anything away from the GPU.'

 

[bill001g]

I am not so sure the motherboard is the issue. You have to look at the total PCIE lanes the CPU chip itself supports. If you really care about the speed you do not want to consider PCIE lanes provided by the chipset rather than the CPU itself.

So the new intel chips have 4 extra pcie 5 lanes. I have not seen if the chip supports splitting the these extra 4 into 2x2 or if it only as a single pcie5 x4. The previous generation intel chips had all 16 pcie5 lanes for the video card with the option to split it into 2x8 but no other options. So you had to give up 1/2 your pcie lanes to get any on a SSD slot.

AMD has more pcie5 lanes but I never bothered to see if it has the same limitation as intel but I suspect it does.

 

[MnsoonMally]

Indeed, it maybe the case, that 2 x PCIe5.0 SSD's are not supported AT ALL, without taking lanes from the GPU.

*which would simplify my search to 1 x PCIe5.0 and multiple PCIe4.0 instead.
**and would give me many more options of choice of Motherboard.

 

[bill001g]

There was quite a bit of discussion when the pcie5 SSD came out how to run multiple.

What it seems is you run it 2x8 and then use a PCIE card to split the second 8 into 2x4 so you can run 2 pcie5 SSD. Running a graphics card at 2x8 does not seem to cause a limitation. Even a 4090 only runs PCIE4 so when you change the machine into 2x8 it run PCIE4 x 8. What they found is you almost can not detect any difference running a 4090 with only 1/2 the lanes. So if we were to assume the new 5090 can run 2 times as fast, highly unlikely, it should be able to run PCIE5 with only 8 lanes with no trouble.

 

[MnsoonMally]

There was quite a bit of discussion when the pcie5 SSD came out how to run multiple.

What it seems is you run it 2x8 and then use a PCIE card to split the second 8 into 2x4 so you can run 2 pcie5 SSD. Running a graphics card at 2x8 does not seem to cause a limitation. Even a 4090 only runs PCIE4 so when you change the machine into 2x8 it run PCIE4 x 8. What they found is you almost can not detect any difference running a 4090 with only 1/2 the lanes. So if we were to assume the new 5090 can run 2 times as fast, highly unlikely, it should be able to run PCIE5 with only 8 lanes with no trouble.

Yes, a lot is written about it. I'm finding the manual's less than clear - even though they do point out sockets with shared lanes.

I'd like to have the capability of running a PCIe5.0 GPU at full x16 bandwidth; either now, or in the future lifetime of the system.
Ideally, with 2 x PCIe5.0 SSD's, unthrottled, non-GPU sharing lanes.



I'm not sure the Z890 architecture supports the above; I think, as far as I can identify, this is the Maximum and Optimal configuration (below):

1 x PCIe5.0 x 16 for the GPU
1 x PCIe5.0 x (?) for an SSD
X x PCIe4.0 x 4 for multiple SSD's

If I can get a definitive answer..........I can stop hurting my head with more research, and just accept it.

 

[MnsoonMally]

I'm looking for a definitive answer, please, to validate my thinking, before I delve into choosing a Z890 Motherboard for a new build:

Given that Z890 architecture supports 20 x PCIe5.0 lanes, and 24 x PCIe4.0 lanes.

Assuming the GPU, either now, or in the future, uses the full 16 x PCIe5.0 lanes:


Only 1 x PCIe5.0 SSD can function, in the appropriate M.2 slot.

Up to 6 x PCIe4.0 SSD's can be connected, in the relevant M.2 slots.

THERE IS NO WAY A SECOND PCIe5.0 SSD CAN BE CONNECTED, AND OPERATE AT GEN 5 SPEED, WITHOUT TAKING LANES ALLOCATED TO THE GPU.


*I'm aware Gen5 SSD's can be utilised in Gen4 Slots, but they will work at Gen4 speeds.

 

[rgd1101]

correct.
cpu only have total of 20 pcie 5.0. chipset only have pcie 4.0

unless there 3rd party chipset for it. which I haven't see any

 

[MnsoonMally]

Awesome - thank-you so much for confirming.

It means I can stop looking for Mobo's supporting 2 x PCIe5.0 SSD's (unthrottled somehow) that don't/can't exist.

It widens my search a lot, as a lot of Mobo's support 1 x PCIe5.0 and multiple PCIe4.0.

Now to check RAM and USB support on them.....